The present invention relates to firearm breech bolt assemblies, and more particularly, but not exclusively, relates to enhancement of breech bolt reliability.
The M-16 automatic rifle has been a standard weapon of choice for the U.S. Military. The M-16 family of weapons includes semi-automatic counterparts which are popular with the civilian sector. Generally, the M-16 family of automatic and semi-automatic firearms are based on a gas operated breech bolt carrier system. As used herein, "gun" or "firearm" refers to a completely assembled weapon including not only a receiver operable to fire rounds of ammunition, but also any other structure normally associated with the given weapon. U.S. Pat. Nos. 2,951,424 and 3,198,076 to Stoner provide early examples of the M-16 type of weapon. In recent years, many variations and modifications of the M-16 family have evolved.
Generally, for the current M-16 weapon family, the bolt carrier system includes a multi-lug breech bolt which interlocks within the gun receiver for firing each round of ammunition. The reaction force from firing a round is transmitted from the breech bolt through the lugs and results in the "recoil" force experienced by the marksman. In one common configuration of the M-16 weapon, a steel "barrel extension" is used to interface with the gun barrel and interlock with the lugs of the breech bolt. Generally, the barrel extension contains pressurized gases resulting from firing of the weapon, and transmits the familiar recoil force. As used herein, a "receiver" includes a barrel extension, barrel interface, or any other part or assembly of a gun or firearm that has one or more surfaces configured to engage lugs of a breech bolt.
Regardless of the receiver configuration, breech bolts are typically subjected to repeated stress from firing the gun. Occasionally, the breech bolt fails from fatigue induced by this repeated stress. These failures limit the overall reliability of the weapon, sometimes represented as Mean-Time-Between-Failure (MTBF). By reducing the frequency of these failures, maintenance actions for the gun are correspondingly reduced and overall reliability is improved. Consequently, there is a need to better accommodate stress imposed on the breech bolt from firing the weapon.